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Prior exposure to the seasonal flu vaccine boosts the effectiveness of the H1N1 vaccine in ferrets, according to new research published in Science Translational Medicine. The findings may influence the ongoing H1N1 vaccination campaign, particularly for children or those with weak immune systems.

Currently, mass vaccination against the virus responsible for the first influenza pandemic of the century—H1N1—is being implemented globally. Yet little is known about how previous seasonal flu vaccination affects H1N1 vaccines. Under extreme time pressure, public health officials have made their best guesses about the appropriate H1N1 vaccine formula and dosage to speed up manufacturing.

Lacking comprehensive clinical trial information, Giuseppe Giudice from Novartis Vaccines and Diagnostics and colleagues from ViroClinics Biosciences and Erasmus University in the Netherlands now report the next best thing: a test in ferrets given the H1N1 virus.

Ferrets are believed to be a reliable animal for modeling the efficacy of influenza vaccines in humans. In the study, researchers gave groups of ferrets doses of the regular seasonal flu vaccine a month prior to H1N1 vaccination.

They found that ferrets supplied with the seasonal flu vaccine before receiving the H1N1 vaccine showed stronger antibody responses when exposed to the virus than ferrets vaccinated for H1N1 alone—and that these responses were greatest when the ferrets had been given a seasonal vaccine with an adjuvant (a substance commonly added to vaccines to improve immune response).

Taking a closer look, the authors discovered that a higher concentration of antibodies present in the ferrets corresponded directly to increased protection from H1N1 infection.

While it is not exactly clear how the seasonal flu vaccine enhances the immune response and efficacy of the H1N1 vaccine in animals (or if this effect holds true in humans) the results are good news for control of the pandemic, as they suggest that the many recipients of the seasonal flu vaccine may be better protected if they also get the H1N1 vaccine.